Acoustophoresis is the separation of particles and secondary fluids from a primary or host fluid using high intensity acoustic standing waves, and without the use of membranes or physical size exclusion filters. It has been known that high intensity standing waves of sound can exert forces on particles in a fluid when there is a differential in both density and/or compressibility, otherwise known as the acoustic contrast factor. The pressure profile in a standing wave contains areas of local minimum pressure amplitudes at its nodes and local maxima at its anti-nodes. Depending on the density and compressibility of the particles, they will be trapped at the nodes or anti-nodes of the standing wave. The higher the frequency of the standing wave, the smaller the particles that can be trapped due to the pressure of the standing wave. The acoustophoretic process is typically performed on a moving fluid stream.
There are many applications where there is a need to clarify a fluid that contains particles or droplets, or separate the secondary phase from the host fluid. In certain situations it can be advantageous to execute such a process in a batch or semi-batch mode, especially when the concentration of the secondary phase is large, e.g., exceeding 1% by volume concentration, or e.g., exceeding 10%. Applications are in settling tanks, yeast separation processes in food and beverage industries, mammalian cell clarification in biopharmacy, and red and white blood cells from plasma.